194 



ARMATURE CONSTRUCTION 



the armature side by side. Thus in Fig. 232 we have two coils, 

 one for each phase, within the pole pitch not overlapping, as in 

 Fig. 227, but placed side by side. Comparing with Fig. 227, the 

 coils are much narrower, and hence their designation "short 

 coils. " Also, in Fig. 233, we have three coils within a double pole 

 pitch. If for the moment we ignore the poles in Fig. 232, and 

 imagine all the coils coloured black and connected in series, then 

 we have a single-phase armature, and the number of poles will 

 necessarily be twice what it was originally. 



U!LJ 



FIG. 233. Six-pole, Three-phase, Short-coil Winding. 



It follows that any single-phase coil-wound armature may be 

 connected up as a two-phase short-coil winding if the total number 

 of coils is a multiple of 2, and as a three-phase short-coil winding 

 if the total number of coils is a multiple of 3. The number of 

 poles as two-phase is one-half the number of poles as single-phase, 

 and, as three-phase, one- third the number as single-phase. Con- 

 versely, any polyphase short-coil winding may be connected for 

 single phase provided there is an even number of coils. The 

 number of poles as single phase will be equal to the number of coils. 



In the short-coil windings the mean length of the turn of a 

 coil is reduced, and, consequently, the total length of conductor per 



